This invention relates to wireless multiple access communications systems and, more particularly, to proper data reception in such systems.
In wireless communications systems employing multiple access, users share a transmission medium. One such wireless system is the orthogonal frequency division multiplexing (OFDM) based spread spectrum multiple access mobile communications system. In such systems, it is important that users are prevented from receiving packets meant for other users. So-called fixed channel assignment techniques have been employed to address this problem by allocating channels that are dedicated to individual users. Unfortunately, such fixed channel assignment of communications channels is not efficient for data traffic. In Ethernet systems, packets are transmitted with identification numbers of the users they are intended for so that other users can drop the packets after they are decoded. The cost of such a technique is the overhead needed to transmit a user identification number in each packet that is substantial in, for example, wireless multiple access communications systems.
These and other problems related to the correct and proper reception of data at a receiver in a multiple access communications system are overcome by processing data to be transmitted to a particular end-user receiver with a specific process assigned to the particular end-user. The processing at a transmitter is such that an output array of data bits after processing has the same number of bits as an input array of data bits but is unique to the particular end-user. Then, the data is only recoverable at the end-user receiver by using a process that is the exact inverse of the process employed at the transmitter and assigned to the particular end-user receiver. Consequently, the data is identified to the particular end-user without having to transmit additional identification information.
In an embodiment of the invention, information bits, e.g., a segment of bits, to be transmitted are encoded to provide an error detection capability at a remote receiver. The encoded segment of bits, i.e., an array of bits, is then processed using a particular end-user dependent function of the encoded array of bits and associated with a user dependent index to generate an output array of bits the same size as the encoded array of bits. The output array of bits is modulated and transmitted. At a remote end-user unit, a received version of the transmitted signal is demodulated to obtain a received array of bits. An exact inverse end-user function of the encoded array of bits and associated with the user dependent index corresponding to the end-user function used at the transmitter is employed to de-map the array of received bits to obtain a received version of the encoded array of bits. This encoded array of bits is decoded, and if it is an array of bits intended for this particular end-user it is properly decoded and accepted. If the decoded array of bits were not intended for this particular end-user, it would not be properly decoded and is dropped.
In another embodiment of the invention, the user dependent function is of only redundancy bits generated by error detection encoder and associated with the user dependent index. Specifically, in one example, the transmitter user dependent function is of the bits of a frame check sum (FCS) sequence generated by a FCS encoder and associated with the user dependent index. The receiver user dependent function is the inverse function of the bits of a frame check sum (FCS) sequence and associated with the user dependent index.